PT16.S2.Q21 - several years ago, as a measure

Martin01

Hey, could someone help explain in detail why A is the correct answer choice? I am still lost. Thank you.

inactive

Bump!

Creasey LSAT

I'll give it a shot. This is a tricky one. Since this is strengthen question, we're looking for an answer that does one of three things: 1. Provides an example of the same cause and same effect or 2. Provides an example of no cause and no effect or 3. Provides an example that eliminates an alternate cause. If an answers satisfies one of these, it can be said to "strengthen" the conclusion that the decline of gypsy moths is attributable to the presence of the poisonous fungus. (Note: the relevant standard in strengthen questions is not to prove that the conclusion would be true, but would simply make it more likely, even if by a tiny bit.)

I'll eliminate the wrong answers first.

(E) A decline in gypsy populations no greater than in forests without the poison would actually weaken our conclusion. This implies effect (decrease in populations no greater than) without cause (poison). Not what we need. Scratch it.

(D) A decline in oak trees caused by air pollution would also weaken our conclusion. This is an example of an alternate cause (substantial decline in oak tree population) for our effect (gypsy population decline). As stated in the stimulus, gypsy moths depend on these trees for food, so a decrease in trees would blow our poison fungus theory out the door. Scratch it.

(C) Again, this weakens our argument. This time, we are told there has been an INCREASE in gypsy due to a decline of species that prey on the moths. That should be sufficient reason enough to get the hell away from this answer choice!

(B) Irrelevant! Why do we care that it is poisonous to few other species? All we care about is our gypsy moth. Scratch it.

(A) It seems like a really weak and indirect way to strengthen our conclusion, but it works. It's a very weak way to imply same cause, same effect. In other words, if a strain of gypsy moth whose caterpillars are unaffected by the fungus has increased in its share of the total gypsy population, then how did that get to be the case? It implies that those who are affected have diminished in their share of the total population, which (we can argue) is because of the fungal poison!

Not Ralph Nader

@Martin01 Answer choice A strengthen the argument because it reduces the likelihood of a third factor being responsible for the decrease in the gypsy moth population. An increase in the share of total population is the key term. I try to explain its impact using some numbers

we can safely assume (as common sense), if enough number of caterpillars fail to grow up and die before turning into gypsy moth, adult gypsy moth and total gypsy moth population decreases overtime due to natural death.

Lets say before introducing the fungus there were only 100 gypsy moths caterpillars in the world and of those only two of them is from the strain that its caterpillar is not effected by the fungus. We also know that after the introduction the population of all gypsy moths decreased significantly, let's say it was reduced to 10 gypsy moths caterpillars and yet none of our special strain of gypsy moths did not die. In this case the strain that is not effected by the fungus share of population would increase. Answer choice A make it less likely (but not impossible) that a third factor such as food shortage (disappearance of all leaves) in the fungus habitat was the reason for decreased population because if that was the case, chances were at least one of our special fungus caterpillar would have died out of hunger.

Keep in mind the argument is not valid even with answer choice A, and the question is not asking you to make it valid, it asks only to strengthen the argument, so be comfortable with answers that increases the likelihood of the argument conclusion being true but does not make it hundred percent right.

I hope this helps. Hopefully other people will explain answer choice A in a simpler way.